1. Field of the Invention
The invention concerns diesel particulate traps and is particularly concerned with making them more economical to manufacture and use, more efficient, and more durable.
2. Description of the Related Art
Diesel engines emit a sooty exhaust that can be rendered less hazardous by diesel particulate traps, but few such engines are so equipped. Known diesel particulate traps unduly increase fuel consumption, tend to be inefficient, and have short useful lives.
There are four main types of diesel particulate traps, each of which can have an elongated tubular casing and means for connecting the ends of the casing into an exhaust system. Of those:
a first type employs a ceramic wallflow monolith such as is described in Offenlegungsschrift No. DE 38 06 131 (Giebling) that was laid open Aug. 31, 1989; PA1 a second type employs a rigid ceramic foam such as are shown in U.S. Pat. Nos. 4,264,346 (Mann) and 4,813,231 (Bykowski); PA1 a third type employs one or more rigid, hollow, perforated, metal tubes such as shown in U.S. Pat. No. 4,324,572 (Erdmannsdoerfer); and PA1 a fourth type employs a mass of fibrous filter material.
Each type can be periodically regenerated during use by burning off the collected particulate matter.
In a diesel particulate trap of the fourth type shown in FIGS. 1 and 2 of Offenlegungsschrift No. 35 45 762 (Brich) which was laid open Feb. 7, 1987, a ceramic fiber mat and a metallic web are spirally wound to provide a filtering element in the form of a mass of fibrous filter material that radially fills a tubular casing. That casing plus inlet and outlet cones provide a canister for the diesel particulate trap. Inlet and outlet endplates have openings that are axially offset so that exhaust gases flow radially outwardly through the filtering element. As is discussed in the Brich Offenlegungsschrift, exhaust gases can produce fiber shedding of fibrous filter material and consequently an undesirably shortened useful life, but this is said to be minimized by interleaving a ceramic fiber mat with a metallic mat so that the two become intermeshed.
Also of the fourth type is the diesel particulate trap of Offenlegungsschrift No. DE 38 01 634 (Stoepler et al.) that was laid open Aug. 3, 1989. The filtering element of its FIGS. 1 and 2 consists of a filter material (12) sandwiched between two perforated metal sheets (13) and (14) that can instead be metallic weaves. The filter material (12) can be a metallic weave or ceramic fibers in the form of a nonwoven mat, a woven structure, or a blanket- or felt-like structure. The sandwich is spirally wound together with corrugated sheets (15) that provide spiral inlet and outlet channels between adjacent convolutions of the filter material, thus providing a filtering element in the form of a mass of fibrous filter material that radially fills a tubular casing.